From: daniel.lezcano@linaro•org (Daniel Lezcano)
To: linux-arm-kernel@lists•infradead.org
Subject: cpu_relax in busy loops question
Date: Thu, 02 Feb 2012 09:47:23 +0100 [thread overview]
Message-ID: <4F2A4D9B.7070302@linaro.org> (raw)
In-Reply-To: <CACRpkdZfdx9tDgp8HfVSdEFXdvpsPDiWdpg2iyFYesgpBjsqyw@mail.gmail.com>
On 02/01/2012 09:17 PM, Linus Walleij wrote:
> On Wed, Feb 1, 2012 at 12:34 PM, Daniel Lezcano
> <daniel.lezcano@linaro•org> wrote:
>>
>> Hi Linus,
>>
>> While looking at the drivers/mfd/db8500-prcmu.c file I noticed:
>>
>>
>> 595 /* Grab the HW semaphore. */
>> 596 while ((readl(PRCM_SEM)& PRCM_SEM_PRCM_SEM) != 0)
>> 597 cpu_relax();
>>
>>
>> I was wondering why is cpu_relax needed here as readl does a memory barrier
>> ? I thought the cpu_relax function was related to the x86 to consume less
>> power with an optimization of the "rep nop" loops or/and do a memory
>> barrier.
>>
>> Should a busy-loop be always with cpu_relax ?
>
> Last time we discussed it ar LAKML I think we came to the conclusion
> that while cpu_relax() has very little semantic meaning on ARM, it
> is still nice to have from a readability and maintenance point of view,
> since it is pretty clear what we're trying to do.
Ok, thanks Linus.
-- Daniel
--
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prev parent reply other threads:[~2012-02-02 8:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-01 11:34 cpu_relax in busy loops question Daniel Lezcano
2012-02-01 20:17 ` Linus Walleij
2012-02-02 8:47 ` Daniel Lezcano [this message]
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